Coatings are effective for improving the performance of various materials, such as for achieving better wear resistance and corrosion resistance. Common applications where a coating is applied to a substrate to improve wear resistance of the substrate material include cutting tool inserts for the cutting of hard materials, such as hardened steels. Common substrate materials for cutting tools may include, for example, hard metals formed of different particle sizes, with a varied percentage of cobalt or nickel as a binder material.
It is often desirable to produce a cut or formed material that has a relatively smooth cut edge. It has generally been believed that in order to produce the smoothest cut edge on a workpiece, the cutting tool insert should have a smooth cutting edge surface, preferably a polished smooth cutting edge surface. In the case where the cutting tool insert has a coating of a hard or superhard material applied to a substrate, it has been believed that it is desirable to produce a smooth or polished edge surface on this coating. Serrated edges on cutting tools or cutting tool inserts have been generally believed to result in a rougher surface finish on the workpiece. For these reasons, it has generally been believed that the coating on a coated-substrate cutting tool insert should be applied in as smooth and even a process as possible, so that the cut resulting from the use of such cutting insert will be desirably smooth. It has further been seen as desirable to provide an additional polishing step at the cutting edge of the coating after the coating deposition process is completed, in order to provide an even smoother edge for cutting, thereby resulting in an even more smoothly cut workpiece.
While smoothly polished cutting edges are generally seen as desirable, the art does include attempts to produce cutting tools with serrated cutting edges. These are primarily intended for use in non-metallic cutting applications. In some cases, however, serrated cutting edges have been employed on tool inserts for metal-cutting applications, although as noted above, this is generally seen as a compromise of poorer (rougher) surface finish in favor of higher metal removal rates. U.S. Pat. No. 7,591,614 to Craig provides one such example of a cutting tool insert with serrations. In such cases, however, the cutting tools or cutting tool inserts have a cutting edge that has precisely designed and manufactured serrations, which as a result of their precise configuration lie in periodic patterns. The application of these periodic patterns of serrations in the manufacture of the cutting tool or cutting tool insert is time consuming, thereby increasing the cost of a cutting tool or cutting tool insert produced in this manner. Cutting tools and cutting tool inserts that provide a smooth cut—particularly with very hard materials such as hardened steels—yet which may be produced relatively quickly and therefore inexpensively, are highly desired.